1. Field of the Invention
The present invention relates to a method of manufacturing a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by using a perpendicular magnetic recording system.
2. Description of the Related Art
Recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, as compared with the longitudinal magnetic recording system.
One of known magnetic heads for the perpendicular magnetic recording system is a single-pole head that applies to a recording medium a magnetic field in a direction perpendicular thereto by using a single main pole. The single-pole head comprises the main pole and an auxiliary pole facing toward each other with a specific distance therebetween in a medium facing surface that faces toward the recording medium. The main pole and the auxiliary pole are coupled to each other at their respective portions located away from the medium facing surface. The single-pole head further comprises a gap layer disposed between the main pole and the auxiliary pole, and a coil at least a portion of which is disposed between the main pole and the auxiliary pole and insulated from the main pole and the auxiliary pole. The main pole includes a track width defining portion and a wide portion, for example. The track width defining portion has an end located in the medium facing surface and defines a track width. The wide portion is coupled to the other end of the track width defining portion and has a width greater than that of the track width defining portion. For example, the wide portion is equal in width to the track width defining portion at the boundary between the wide portion and the track width defining portion, then gradually increases in width with increasing distance from the medium facing surface, and then the width finally becomes constant.
What are required of magnetic heads for achieving higher recording density are a reduction in track width, that is, a reduction in width of the main pole taken in the medium facing surface, and an improvement in writing characteristics, in particular. However, a reduction in track width results in degradation in writing characteristics, such as an overwrite property that is a parameter indicating an overwriting capability. It is therefore required to achieve better writing characteristics as the track width is reduced.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface that faces toward the recording medium. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks. In a magnetic disk drive, the skew may cause such a phenomenon that, when data is written on a specific track, data stored on a track adjacent thereto is erased. This phenomenon is hereinafter called “adjacent track erasing”. To achieve higher recording density, it is also required to suppress adjacent track erasing.
For magnetic heads for the perpendicular magnetic recording system, possible methods for improving the overwrite property include: a method in which the boundary between the track width defining portion and the wide portion of the main pole is made closer to the medium facing surface; a method in which the angle formed between a side surface of the track width defining portion and a medium-facing-surface-side end face of the wide portion is made closer to 90 degrees; and a method in which the main pole is increased in thickness. However, each of these methods is likely to cause adjacent track erasing.
To prevent adjacent track erasing when a skew occurs, Japanese Unexamined Patent Application Publication No. 2002-92821 discloses a technique in which an end face of the main pole located in the medium facing surface is made to have a shape of trapezoid in which the side located backward in the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side. However, this leads to degradation in overwrite property because the end face of the main pole located in the medium facing surface is reduced in area as compared with a case in which the end face is rectangle-shaped.
Accordingly, for preventing adjacent track erasing and also improving overwrite property, there have been proposed various techniques in which the thickness of the main pole is decreased with decreasing distance from the medium facing surface, as disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 2002-133610, 2002-197615 and 2003-6811 (hereinafter referred to as JP-A-2002-133610, JP-A-2002-197615 and JP-A-2003-6811, respectively).
JP-A-2002-133610 discloses a technique in which at least one of top and bottom surfaces of the main pole is slanted near the medium facing surface, so that a portion of the main pole near the medium facing surface is decreased in thickness with decreasing distance from the medium facing surface.
JP-A-2002-197615 discloses a technique in which a yoke layer whose front-end face is located away from the medium facing surface is connected to a main pole layer having a constant thickness, so that the layered structure made up of the main pole layer and the yoke layer decreases in thickness with decreasing distance from the medium facing surface.
JP-A-2003-6811 discloses a technique in which, in a magnetic layer constituting the main pole, one of two surfaces closer to the gap layer is formed to have a such shape that the surface of the magnetic layer gets closer to the auxiliary pole stepwise with increasing distance from the medium facing surface, so that the thickness of the main pole decreases with decreasing distance from the medium facing surface.
According to the technique disclosed in JP-A-2002-133610, in the course of manufacturing the magnetic head, if the point at which polishing is stopped is shifted when forming the medium facing surface by polishing, the thickness of the main pole taken in the medium facing surface is varied. Therefore, according to this technique, it is difficult to mass-produce uniform magnetic heads.
According to the technique disclosed in JP-A-2002-197615, the main pole layer is formed on the yoke layer, and these layers are individually patterned. As a result, misalignment of the yoke layer and the main pole layer is likely to occur. According to the technique, in particular, a portion of each of the yoke layer and the main pole layer near the medium facing surface has a width smaller than that of the other portion. Accordingly, misalignment of these portions having smaller widths could cause degradation in writing characteristics of the magnetic head. Furthermore, according the technique, the top surface of the yoke layer is flattened, and the main pole layer is formed thereon. Therefore, if the point at which polishing is stopped is shifted when flattening the top surface of the yoke layer by polishing, the position of one of ends of the yoke layer closer to the medium facing surface is varied. Consequently, according to this technique, it is difficult to mass-produce uniform magnetic heads.
According to the technique disclosed in JP-A-2003-6811, the shape of the top surface of a base layer for the magnetic layer constituting the main pole is determined by dry etching using a mask. Therefore, according to this technique, the point at which the thickness of the magnetic layer starts to decrease is determined by the position of the boundary between the bottom surface and the side surface of the recess formed by the dry etching. In this case, the position of the boundary between the bottom and side surfaces of the recess will vary by about ±0.15 μm. It is thus difficult to precisely control the point at which the thickness of the magnetic layer starts to decrease. Consequently, according to this technique, it is difficult to mass-produce uniform magnetic heads.